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Which operation are allowed in a join view:

  • Q.

    Which operation are allowed in a join view:

  • filter_dramaExplanation
    Answer is : D

    The DELETE statement is used to delete rows in a table. The UPDATE statement is used to update existing records in a table. The INSERT INTO statement is used to insert new records in a table.

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Similar Questions

  • 1.

    In RDBMS, which type of Join returns all rows that satisfy the join condition ?

  • filter_dramaExplanation
    Answer is : A

    Concept:

    Join operation is used to combine related tuples from two relations into single tuples. Join operation can be stated in terms of Cartesian product followed by SELECT operation.

    Join condition form: ANDAND……AND

    Explanation:

    There are various variations of join operations such as equi-join, natural join, theta join, inner join, outer join.

    • Natural join is performed by equating all attributes pairs that have the same name in the two relations.
    • Join operation with equality condition is known as equi-join.
    • Join operation which is used to combine data from multiple relations so that related information can be presented in a single table is known as inner join. Inner join is a type of match and merge operations defined as combination of Cartesian product and selection.
    • Outer join can be used when we want to keep all the tuples in the result of join regardless of whether or not they have matching tuples in other relation.
  • 2.

    Which of the following Relational Algebra operations can be used when you want to keep all the tuples of the first relation irrespective of whether or not they have matching tuples in the second relation?

  • filter_dramaExplanation
    Answer is : B

    The answer to the above question is Option 2) Left-outer Join
    A JOIN clause is used to combine rows from two or more tables, based on a related column between them.

    Here are the different types of the JOINs in SQL:

    1. (INNER) JOIN: Returns records that have matching values in both tables
    2. LEFT (OUTER) JOIN: Returns all records from the left table, and the matched records from the right table
    3. RIGHT (OUTER) JOIN: Returns all records from the right table, and the matched records from the left table
    4. FULL (OUTER) JOIN: Returns all records when there is a match in either left or right table

    We can see that left join keeps all the elements from the first relation irrespective of their presence in second relation.

  • 3.

    Given two tables R1(x, y) and R2(y, z) with 50 and 30 number of tuples respectively. Find maximum number of tuples in the output of natural join between tables R1 and R2 i.e. R1 * R2? (*. Natural Join)

  • filter_dramaExplanation
    Answer is : D

    Concept:

    A natural join is based on common attributes or common columns to join two tables or relations.

    Explanation:

    Consider an example, suppose there are two tables Employee(Eid, Ename) consists of 5 tuples and department(Eid, Did) consists of 3 tuples only.

    Eid

    Ename

    1

    E1

    1

    E2

    1

    E3

    1

    E4

    1

    E5

     

    Eid

    Did

    1

    D1

    1

    D2

    1

    D3

     

    Natural join of employee and department(Employee * Department) gives:

    5 × 3 = 15

    So, maximum number of tuples in natural join are from the relation having minimum tuples. So, in given question, R2 contains 30 tuples, so , maximum number of tuples in the output of natural join between tables R1 and R2 i.e. R1 * R2 = 50 × 30 = 1500.

  • 4.
    SELECT *
      FROM student JOIN takes USING (ID);

    The above query is equivalent to

  • filter_dramaExplanation
    Answer is : A

    Join can be replaced by inner join.

  • 5.

    Which join refers to join records from the write table that have no matching key in the left table are include in the result set:

  • filter_dramaExplanation
    Answer is : B

    A right outer join will return all the rows that an inner join returns plus one row for each of the other rows in the second table that did not have a match in the first table. It is the same as a left outer join with the tables specified in the opposite order.

    Outer joins are of following three types.

    1. Left outer join
    2. Right outer join
    3. Full outer join

    Right Outer Join : The right join operation returns all record from right table and matching records from the left table. On a matching element not found in left table, NULL is represented in that case.

     

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